I'm thinking more at an SMB level, not necessarily for secure mail, PGP and the like.

IMAP + CalDev + CardDev sat on-top of cPanel is getting a bit long in the tooth for companies that want exchange-like mail solutions outside of the big two. Unfortunately MS and Google run the "spam" filters as well, so you really need an established company that they can't afford to irritate to enter the space - see Mozilla - to reliably force acceptance of enterprise mail outside the Duopoly they have.

Zoho is trying their best also in this space - not sure how successful they have been on the trusted email provider and integration front.